Recently, because of environmental problems, it has been strongly desired to reduce the amount of volatile organic solvents used. To meet this demand, trials have been performed in which organic solvent-based compositions containing a polyisocyanate were replaced by water-based compositions. For example, Japanese Examined Patent Application, Second Publication No. Sho 55-7472 and U.S. Pat. No. 5,252,696 (corresponding to Japanese Unexamined Patent Application, First Publication No. Hei 5-222150) describe polyisocyanate compositions wherein a portion of the polyisocyanate is modified with a polyoxyalkylene glycol whose one terminal is blocked with an alkoxy group. When these compositions are dispersed in water, there arises a problem that the reaction between isocyanate groups in the polyisocyanate and water is liable to occur and isocyanate groups are rapidly consumed by this reaction. A curable composition comprising such a polyisocyanate composition and a water-based resin having an active hydrogen group-containing group has a short pot life and also has drawbacks that a cured material obtained form such a curable composition is inferior in hardness and water resistance.
Japanese Unexamined Patent Application, First Publication No. Hei 7-113005 describes a polyisocyanate composition having an improved water dispersibility, which is obtained by modifying a portion of isocyanate groups in the polyisocyanate with a polyoxyalkylene glycol whose one terminal is blocked with an alkoxy group, and an aliphatic compound having a hydroxyl group or a fatty acid ester. A dispersion obtained by dispersing this polyisocyanate composition in water has a slightly improved stability of isocyanate groups to water, but has insufficient dispersibility in water and poor workability. Also a curable composition comprising the polyisocyanate composition and a water-based resin having an active hydrogen group-containing group has a short pot life and the resulting cured material is also inferior in hardness and water resistance.
Japanese Unexamined Patent Application, First Publication No. Hei 9-71720 describes a polyisocyanate composition obtained by adding an ionic emulsifier to a polyisocyanate obtained by modifying a portion of isocyanate groups with a polyoxyalkylene glycol whose one terminal is blocked with an alkoxy group. In such a composition, the water dispersibility and stability of isocyanate groups to water are slightly improved but are not satisfactory. Since a composition comprising the polyisocyanate composition and a water-based resin having an active hydrogen group-containing group contains an ionic emulsifier, the resulting cured material is inferior in hardness and water resistance.
Japanese Unexamined Patent Application, First Publication No. Hei 1-168716 discloses a method of dispersing a polyisocyanate using a dispersant having no isocyanate group obtained by reacting a polyisocyanate with a polyoxyalkylene glycol whose one terminal is blocked with an alkoxy group, a higher alcohol having 8 or more carbon atoms, a fatty acid ester having an active hydrogen group-containing group wherein fatty acid has 8 or more carbon atoms, and a polyoxypropylene monoalkyl ether.
Japanese Unexamined Patent Application, First Publication No. Hei 9-104814 discloses a polyisocyanate composition comprising a polyisocyanate and a dispersant having no isocyanate group, which is obtained by reacting a polyisocyanate with a polyoxyalkylene glycol whose one terminal is blocked with an alkoxy group and an aliphatic compound having an active hydrogen group-containing group such as a higher alcohol. When the composition obtained by the method disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 1-168716 or the composition disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 9-104814 is dispersed in water, the stability of isocyanate groups to water is comparatively good. However, since the composition comprising the polyisocyanate composition and the water-based resin having an active hydrogen group-containing group has poor compatibility because it contains a dispersant having no isocyanate group, there are drawbacks that the resulting cured material is inferior in appearance, hardness and water resistance.
Japanese Unexamined Patent Application, First Publication No. Hei 6-239957 describes a polyisocyanate composition comprising a polyisocyanate, a portion of which is modified with a polyoxyethylene glycol whose one terminal is blocked with an alkoxy group, and an acrylic polymer having an isocyanate group. Such a composition has problems that the stability of isocyanate groups to water is insufficient and a curable composition made of a water-based resin and the polyisocyanate composition has a short pot life and the resulting cured material is inferior in water resistance.
Japanese Unexamined Patent Application, First Publication No. 2000-191743 discloses a polyisocyanate composition obtained by modifying with an ionic surfactant containing an active hydrogen and a nonionic surfactant containing an active hydrogen. Such a composition has sufficient water dispersibility, but is insufficient in stability of isocyanate groups to water. Also, a curable composition comprising such a composition and a water-based resin having an active hydrogen group-containing group has a short pot life and has a drawback that the cured material is inferior in hardness and water resistance.